In recent years, a variety of projectors have been widely used in various applications because projectors have many benefits such as small volume, portability and the production of enlarged images. For example, projectors can be used for making presentations, holding meetings or giving lectures in conference rooms or home theaters. For enhancing stability and marketing competition of the projector, it is important to maintain or prolong the life span of a lamp of the projector. In addition to the production quality of the lamp, the design of a heat dissipating mechanism of the projector has influence on the life span of the lamp. During operations of the projector, a great amount of heat is generated by the lamp. Generally, the projector is equipped with a fan device for removing the heat.
Nowadays, the light sources used in most projection systems are for example ultra-high pressure (UHP) mercury lamps. However, the use of the UHP mercury lamp may result in some drawbacks. FIG. 1 schematically illustrates the situation of condensing mercury vapor on an electrode of a UHP mercury lamp. FIG. 2 schematically illustrates the situation of condensing mercury vapor on an interior glass surface of the UHP mercury lamp. As shown in FIGS. 1 and 2, mercury 10 and some chemical substances (not shown) are contained in the UHP mercury lamp 1. When the UHP mercury lamp 1 is turned on, the mercury 10 in a vapor phase reacts with the chemical substances to continuously generate light. In case that the projector is switched from a working state to a power-off state, the UHP mercury lamp 1 is turned off. Since the mercury 10 has a condensation point of about 300° C., after the UHP mercury lamp 1 is turned off, the mercury 10 is changed from the vapor phase to a liquid phase. Generally, the mercury 10 may be condensed and adsorbed on an electrode 11 of the lamp burner of the UHP mercury lamp 1 (see FIG. 1), or the mercury 10 may be condensed and adsorbed on an interior glass surface 12 of the UHP mercury lamp 1 (see FIG. 2). The condensation position of the mercury 10 after the UHP mercury lamp 1 is turned off may be determined according to the cooling rate of the electrode and the cooling rate of the glass. Generally, in case that no measure is taken, the cooling rate of the electrode is faster than the cooling rate of the glass. After the fan device is switched from the working state to the power-off state, the fan device is still enabled to remove heat from the UHP mercury lamp 1. Under this circumstance, the cooling rate of the glass is faster than the cooling rate of the electrode. For increasing the life span of the UHP mercury lamp of the projector, it is preferred that the mercury vapor is completely condensed on the electrode and the lamp is turned on at the re-ignition temperature. In other words, after the projector is turned off, the lamp should be cooled down to a specified temperature (e.g. lower than 100° C.) and then the lamp may be turned on again.
From the above discussions, after the projector is switched from the working state to the power-off state, the operation of the fan device may influence the cooling time and cooling efficacy of the UHP mercury lamp. That is, the efficacy of condensing the mercury vapor on the electrode and the time period required to re-ignite the lamp are influenced by the operation of the fan device.
The conventional method of controlling the fan device of the projector fails to simultaneously achieve the function of condensing the mercury vapor on the electrode and the function of shortening the time period for cooling the lamp to the re-ignition temperature. In accordance with a conventional control method, the fan device is disabled when the lamp is switched from the working state to the power-off state. Since the cooling rate of the electrode is faster than the cooling rate of the glass, the mercury vapor is almost condensed on the electrode. However, the time period for cooling the lamp to the re-ignition temperature is very long (e.g. 8 minutes). In other words, the conventional method of controlling the fan device of the projector is not efficient.
Therefore, there is a need of providing an improved fan control method for a projection apparatus in order to avoid the above drawbacks.